Hybrid drive system

ABSTRACT

The invention relates to a hybrid drive system comprising an internal combustion engine ( 11 ) which is operated using fuel ( 21 ) from a fuel tank ( 20 ), and comprising a hydraulic machine ( 12 ) which interacts with a hydraulic energy store ( 38 ). In order to provide a hybrid drive system which requires less installation space than conventional hybrid drive systems, the hydraulic machine ( 12 ) is operated with the same fuel ( 21 ) with which the internal combustion engine ( 11 ) is also operated.

BACKGROUND OF THE INVENTION

The invention relates to a hybrid drive system having an internal combustion engine which is operated with fuel from a fuel tank, and having a hydraulic machine which interacts with a hydraulic energy store. The invention also relates to a method for operating a hybrid drive system as described above.

SUMMARY OF THE INVENTION

The object of the invention is to provide a hybrid drive system having an internal combustion engine which is operated with fuel from a fuel tank, and having a hydraulic machine which interacts with a hydraulic energy store, which requires fewer components than conventional hybrid drive systems.

The object is achieved in the case of a hybrid drive system having an internal combustion engine which is operated with fuel from a fuel tank, and having a hydraulic machine which interacts with a hydraulic energy store, in that the hydraulic machine is operated with the same fuel with which the internal combustion engine is also operated. The hydraulic machine is optionally operated as a drive motor or as a pressure pump for the hydraulic energy store, instead of the internal combustion engine. According to one essential aspect of the invention, the hydraulic machine is not operated with a conventional hydraulic fluid but rather with fuel, preferably with diesel fuel. As a result of the consumption of fuel during the operation of the internal combustion engine, it is easily possible to ensure sufficient renewal of the fuel which serves as a hydraulic fluid. A separate equalizing container for hydraulic fluid can be dispensed with.

A preferred exemplary embodiment of the hybrid drive is characterized in that the hydraulic machine is hydraulically connected to the fuel tank of the internal combustion engine and to the hydraulic energy store. According to a further aspect of the invention, the fuel tank is used as an equalizing container for the drive hydraulics. The hydraulic machine can be constructed and configured in a self-priming fashion. The supply of the hydraulic machine in the pump operating mode then occurs directly from the fuel tank.

A further preferred exemplary embodiment of the hybrid drive system is characterized in that a pre-delivery pump is connected between the fuel tank and the hydraulic machine. According to a further aspect of the invention, a pre-delivery pump which is already present in a fuel injection system is used to supply the hydraulic machine with fuel.

A further preferred exemplary embodiment of the hybrid drive system is characterized in that a control unit is connected between the hydraulic machine and the hydraulic energy store. The control unit is preferably a control valve device by means of which the hydraulic machine can be connected to the hydraulic energy store and/or to the fuel tank in such a way that the hydraulic machine is operated either as a hydraulic pump or as a hydraulic motor. The control valve device can also be used only for switching power levels. The pump/motor operating mode can then be set autonomously at the drive machine.

A further preferred exemplary embodiment of the hybrid drive system is characterized in that the control unit is hydraulically connected to a clutch which is connected between the internal combustion engine and the hydraulic machine. The clutch between the internal combustion engine and the hydraulic machine requires rapid closing and controlled opening in the transitions between the individual operating modes. As a result of the integration of the activation of the clutch into the drive hydraulics, the properties of conventional electric operating devices can be surpassed.

A further preferred exemplary embodiment of the hybrid drive system is characterized in that the control unit is hydraulically connected to a hydraulic motor which is connected in terms of drive to a fuel high-pressure pump of a fuel injection system. Although this degrades the overall efficiency level for the generation of the injection pressure in the fuel injection system, it is also surprisingly possible to obtain advantages. For example, the demands made of the fuel high-pressure pump can be reduced by dispensing with an intake throttle. Furthermore, the installation location of the fuel high-pressure pump is freely selectable since the fuel high-pressure pump no longer has to be installed on the internal combustion engine. Furthermore, the fuel high-pressure pump can run separately from the internal combustion engine.

A further preferred exemplary embodiment of the hybrid drive system is characterized in that the control unit is hydraulically connected to one inlet of a, or of the, fuel high-pressure pump. As a result it is possible to supply the fuel high-pressure pump with fuel as a function of requirements, said fuel being pressurized by the hydraulic machine. This provides advantages during rapid starting of the internal combustion engine. By relaxing the fuel from the drive hydraulics it is also possible, if appropriate, for the pre-delivery means of the fuel high-pressure pump to be dispensed with.

A further preferred exemplary embodiment of the hybrid drive system is characterized in that the hydraulic energy store comprises a gas pressure accumulator which is filled with fuel and which can be connected, or is connected, to the fuel tank. The hydraulic energy store is preferably pressurized by means of the hydraulic machine during the pumping operation.

In a method for operating a previously described hybrid drive system, the object specified above is achieved in that the hydraulic machine is operated with the same fuel with which the internal combustion engine is also operated. During operation of the internal combustion engine, the hydraulic machine functions as a pressure pump which is driven by the internal combustion engine. During the motor operation, the hydraulic machine is driven by the hydraulic energy store.

A preferred exemplary embodiment of the method is characterized in that the fuel high-pressure pump of the fuel injection system is supplied with fuel as a function of requirements, said fuel being pressurized, or having been pressurized, by the hydraulic machine. This provides advantages, inter alia, during rapid starting of the internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the invention emerge from the following description in which various exemplary embodiments are described in particular with reference to the drawing.

In the drawing:

FIG. 1 is a highly simplified schematic illustration of a hybrid drive system according to the invention, and

FIG. 2 shows a Cartesian coordinate diagram in which an exemplary profile of the rotational speed of the internal combustion engine and of the rail pressure of the hybrid drive system illustrated in FIG. 1 is plotted against the time.

DETAILED DESCRIPTION

FIG. 1 shows, purely by way of example, a highly simplified schematic illustration of a drive train 1 of a motor vehicle. The drive train 1 comprises a drive axle 2 with two wheels 3, 4, which are driven by means of the drive axle 2. The drive axle 2 can be mechanically coupled to an internal combustion engine 11 through the intermediate connection of a transmission 5, it being possible to drive the drive axle 2 via said internal combustion engine 11. Alternatively, the drive axle 2 can be driven by means of a hydraulic machine 12 which can either be operated as a hydraulic motor or as a hydraulic pump. A clutch 14 by means of which the internal combustion engine 11 can be decoupled from the rest of the drive train 1, is connected between the internal combustion engine 11 and the hydraulic machine 12.

The hybrid drive system 1 also comprises a fuel tank 20, which is filled with fuel 21. The fuel 21 is preferably diesel fuel, which, according to an essential aspect of the invention, is used not only to supply the internal combustion engine 11 but is also employed as a working fluid, in particular a hydraulic fluid, for the hydraulic machine 12.

The fuel 21 is fed through a fuel line 24 to a fuel high-pressure pump 25 using a pre-delivery pump 22 which is arranged, for example, in the fuel tank 20. The fuel high-pressure pump 25 can, however, also be of self-priming design.

The fuel high-pressure pump 25 is part of a fuel injection system, in particular of a diesel injection system. In the fuel high-pressure pump 25, the fuel which is sucked in or delivered from the fuel tank 20 is subjected to high pressure and fed via a fuel high-pressure line 27 to a central fuel high-pressure accumulator 26 which is also referred to as a common rail. The fuel which has been subjected to high pressure is injected from the central high-pressure accumulator 26 into combustion chambers of the internal combustion engine 11 via fuel injection valves 28, which are also referred to as injectors.

The fuel 21 from the fuel tank 20 is also fed to the hydraulic machine 12 via a filter device 31 and a hydraulic line 30. Owing drops in pressure, there was a flow through the filter device 31 only when the fuel was relaxed in the motor operating mode. The hydraulic line 30 can, like the fuel lines 24 and 27 described above and the further hydraulic lines described below, be embodied as a separate line or as a duct which runs at least partially through a housing body. The hydraulic machine 12 is connected to a control unit 35 via a further hydraulic line 34. The control unit 35 is preferably a hydraulic control device which is connected to a hydraulic energy store 38 via a further hydraulic line 36.

In the design outlined in FIG. 1, the rotational speed of the hydraulic machine 12 corresponds, when the clutch 14 is closed, to the rotational speed of the internal combustion engine 11, with the result that corresponding ranges of efficiency have to be taken into account in the configuration. Alternatively, the rotational speed of the internal combustion engine 11 can also be stepped up or stepped down via an intermediately connected transmission.

In the pump operating mode, the hydraulic machine 12 is driven by the internal combustion engine 11, with the result that fuel 21 is delivered from the fuel tank 20 into the energy store 38 via the control unit 35 using the hydraulic machine 12. Depending on the design of the hydraulic machine 12, various circuits can be implemented using the control unit 35. On the one hand, the hydraulic machine 12 can be embodied so as to be self-priming in the pump operating mode. The fluid supply to the hydraulic machine 12 then occurs directly from the fuel tank 20. Alternatively, the hydraulic machine 12 can also be embodied so as to be non-self-priming. According to a further aspect of the invention, the hydraulic machine 12 can then be connected to the pre-delivery pump 22 of the fuel injection system, as indicated by the dashed line 39. The pre-delivery pump 22 is preferably driven electrically. In this case, it is also possible to provide filtering before the fuel enters the hydraulic machine 12. However, the technical implementation of the variant indicated by the dashed line 39 may involve problems since the volume flows which occur for electric pre-delivery systems are relatively large.

If the hydraulic machine 12 is not of self-priming design, the described pre-delivery concept is preferably used. However, in certain situations it is also possible to apply the fuel pressure from the drive hydraulics to the fuel high-pressure pump 25, as is indicated by dashed hydraulic lines 41 and 43. The two hydraulic lines 41, 43 are connected to one another by means of a branching point 42. The control unit 35 is connected to the inlet side of the fuel high-pressure pump 25 via the two hydraulic lines 41, 43. This connection to the drive hydraulics provides advantages in the case of rapid starting of the internal combustion engine. In addition to the time for the synchronization of the crankshaft angle with the camshaft and the actual acceleration of the rotational speed, the minimum rail pressure for enabling the injection determines the starting time. In order to shorten the latter, it is possible, in a way analogous with rail venting, to bypass a high-pressure valve provided in the fuel high-pressure pump 25 by applying the pressure from the drive hydraulics, thereby biasing a sufficient rail pressure.

In addition to the application of pressure described above, it is also possible to stabilize the rail pressure in the vicinity of the working pressure of the drive hydraulics during a stationary state of the internal combustion engine through a simple regulating process. In this context, a considerable advantage can be obtained in terms of the loading on the high-pressure components in the load spectrum, in particular relatively small pressure range pairs can be obtained. In the case of a self-priming hydraulic machine 12 it is also possible for the usual pre-delivery of the fuel high-pressure pump 25 to occur through corresponding relaxing of the fuel from the drive hydraulics. A conventional overflow valve on the fuel high-pressure pump 25 for regulating the pressure of the pre-delivery can therefore be dispensed with.

The drive of the fuel high-pressure pump 25 can be provided mechanically by means of the internal combustion engine 11. However, by virtue of the inventive integration of the drive hydraulics, the drive can also be provided hydraulically via the drive hydraulics themselves. Although this worsens the overall efficiency level for the generation of the injection pressure, the demands made of the fuel high-pressure pump 25 can be reduced by dispensing with suction throttling. In this context it is possible, in particular to reduce the pressure loading and torque peaks. The rotational speed and the size of the fuel high-pressure pump can be freely selected given a corresponding number of delivery elements.

A hydraulic line 44 branches off from the junction 42 and connects the drive hydraulics to a hydraulic motor 45 which, as indicated by a line 46, is connected in terms of drive to the fuel high-pressure pump 25. The fuel high-pressure pump 25 is therefore driven using the hydraulic motor 45 via the drive hydraulics, that is to say the hydraulic machine 12 and/or the hydraulic energy store 38. In this drive concept, it is no longer necessary to install the fuel high-pressure pump 25 on the internal combustion engine 11. Accordingly, corresponding specifications relating to the installation location of the fuel high-pressure pump 25 are dispensed with.

The hydraulic energy store 38 serves to store energy which is generated in a suitable vehicle operating state with the drive hydraulics, that is to say with the hydraulic machine 12. Within the scope of the present invention, a gas pressure accumulator has proven particularly advantageous for this purpose. The gas pressure accumulator provides, inter alia, the advantage that the pressure energy which is made available by the hydraulic machine 12 in the pump operating mode does not have to be converted for storage or for subsequent use. From there, simple integration of a control means for further components occurs by means of the drive hydraulics. Furthermore, rapid charging/discharging gradients are possible. Furthermore the gas pressure accumulator is low in weight and requires little maintenance. In this context, the gas pressure accumulator permits a sufficient storage duration in order to cope with start/stop situations.

The energy flows in the drive hydraulics are controlled by means of the control unit 35. Depending on the operating state and on the storage content of the energy store 38, the operation of the hydraulic machine 12 is regulated as a pump, and the energy storage or the operation of the other hydraulically controlled components is coordinated.

The clutch 14 is connected to the control unit 35 via a further hydraulic line 40. The integration into the drive hydraulics also provides a large potential here. For a starting process with an empty energy store 38, the clutch 14 must be closed in an unactivated fashion. Subsequently, the corresponding actuating energy for optional opening 14 can be made available via the hydraulic machine 12.

FIG. 2 shows, in a Cartesian coordinate diagram, the rotational speed n of the internal combustion engine and the rail pressure p in the central fuel high-pressure accumulator of the fuel injection system plotted against the time t. The rotational speed n and the rail pressure p are constant over time to a stopping time 51 of the internal combustion engine. After the stopping time 51, both the rotational speed n and the rail pressure p decrease linearly over time. In this context, the rotational speed decreases more steeply than the rail pressure. During a time period 54 both the rotational speed and the rail pressure drop to minimum value, for example to zero. At a starting time 52 of the internal combustion engine, the rotational speed increases linearly until it reaches its previous value again. As a result of the inventive hydraulic connection to the hydraulic energy store, the rail pressure already increases before the rotational speed and with a larger gradient than the rotational speed. 

1. A hybrid drive system having an internal combustion engine (11) which is operated with fuel (21) from a fuel tank (20), and having a hydraulic machine (12) which interacts with a hydraulic energy store (38), characterized in that the hydraulic machine (12) is operated with the same fuel (21) with which the internal combustion engine (11) is also operated.
 2. The hybrid drive system as claimed in claim 1, characterized in that the hydraulic machine (12) is hydraulically connected to the fuel tank (20) of the internal combustion engine (11) and to the hydraulic energy store (38).
 3. The hybrid drive system as claimed in claim 2, characterized in that a pre-delivery pump (22) is connected between the fuel tank (20) and the hydraulic machine (12).
 4. The hybrid drive system as claimed in claim 1, characterized in that a control unit (35) is connected between the hydraulic machine (12) and the hydraulic energy store (38).
 5. The hybrid drive system as claimed in claim 4, characterized in that the control unit (35) is hydraulically connected to a clutch (14) which is connected between the internal combustion engine (11) and the hydraulic machine (12).
 6. The hybrid drive system as claimed in claim 4, characterized in that the control unit (35) is hydraulically connected to a hydraulic motor (45) which is drivingly connected to a fuel high-pressure pump (25) of a fuel injection system.
 7. The hybrid drive system as claimed in claim 4, characterized in that the control unit (35) is hydraulically connected to one inlet of a fuel high-pressure pump (25).
 8. The hybrid drive system as claimed in claim 1, characterized in that the hydraulic energy store (38) comprises a gas pressure accumulator which is filled with fuel and which is connected, or can be connected, to the fuel tank (20).
 9. A method for operating a hybrid drive system having an internal combustion engine (11) which is operated with fuel (21) from a fuel tank (20), and having a hydraulic machine (12) which interacts with a hydraulic energy store (38), comprising operating the hydraulic machine (12) with the same fuel (21) with which the internal combustion engine (11) is also operated.
 10. The method for operating a hybrid drive system as claimed in claim 9, further comprising supplying a fuel high-pressure pump (25) of the fuel injection system with fuel as a function of requirements, said fuel being pressurized by the hydraulic machine (12).
 11. The hybrid drive system as claimed in claim 1, wherein the hydraulic machine is driven by the internal combustion engine.
 12. The hybrid drive system as claimed in claim 1, wherein in a pump operating mode, the hydraulic machine pumps fuel from the fuel tank to the hydraulic energy store.
 13. The hybrid drive system as claimed in claim 3, characterized in that a control unit (35) is connected between the hydraulic machine (12) and the hydraulic energy store (38).
 14. The hybrid drive system as claimed in claim 13, characterized in that the control unit (35) is hydraulically connected to a clutch (14) which is connected between the internal combustion engine (11) and the hydraulic machine (12).
 15. The hybrid drive system as claimed in claim 14, characterized in that the control unit (35) is hydraulically connected to a hydraulic motor (45) which is drivingly connected to a fuel high-pressure pump (25) of a fuel injection system.
 16. The hybrid drive system as claimed in claim 15, characterized in that the control unit (35) is hydraulically connected to one inlet of a fuel high-pressure pump (25).
 17. The hybrid drive system as claimed in claim 16, characterized in that the hydraulic energy store (38) comprises a gas pressure accumulator which is filled with fuel and which is connected, or can be connected, to the fuel tank (20). 